Fiber optic bundles are used in a wide variety of optical applications, including optical fiber amplifiers, couplers, splitters and cladding-pumped lasers. In an exemplary application, a fiber bundle is used to couple light from a multiplicity of laser diode light sources to the inner cladding of a double-clad fiber device. The fiber bundle is typically made by fusing together the individual fibers. The bundle may then be tapered, again using a heat treatment, to provide increased light intensity.
To date, the conventional tapered fiber bundles formed using the “fuse and taper” process have at least one serious drawback: the act of tapering decreases the diameter of the central core fiber. As a result, it creates a mismatch in core diameters between the central core of the fiber bundle and the core of the communication fiber (e.g., fiber amplifier) in the device to which the bundle is coupled.
In some cases, when using standard single mode fibers, this problem may be addressed by SMT-type fibers as the central fiber of the tapered fiber bundle. In particular, an SMT fiber comprises a core sitting on a pedestal, where the geometries of the core and pedestal are configured so that when such a fiber is tapered down to a certain diameter, the mode field becomes the same as for an untapered fiber. Alternatively, various types of in-line lensing arrangements may be inserted between the fiber bundle and the communication fiber to improve the coupling efficiency. However, this coupling comes at the cost of requiring additional components, cost and assembly, as well as introducing losses/reflections at the various interfaces between components.
Thus, a need remains in the art for an arrangement utilizing tapered fiber bundles that allows for a conventional core-to-core coupling between the core of the fiber bundle and the core of the communication fiber.